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IDProjectCategoryView StatusLast Update
0017346FPCRTLpublic2019-12-05 16:04
ReporterBenito van der Zander Assigned ToMichael Van Canneyt  
Status resolvedResolutionfixed 
Product Version2.4.0 
Target Version3.2.0Fixed in Version3.0.0 
Summary0017346: unhandled exceptions on stdout
DescriptionUnhandled exceptions are written to stdout, but I think they should be written to stderr.
Stderr is the standard on unix for errors, and if you redirect stdout to a file, you don't get the error messages.
Procedure CatchUnhandledException (Obj : TObject; Addr: Pointer; FrameCount: Longint; Frames: PPointer);[public,alias:'FPC_BREAK_UNHANDLED_EXCEPTION'];
  Message : String;
  i : longint;
  hstdout : ^text;
  hstdout:=@stdout; //<<!!
  Writeln(hstdout^,'An unhandled exception occurred at $',HexStr(PtrUInt(Addr),sizeof(PtrUInt)*2),' :');
  if Obj is exception then
TagsException, output
Fixed in Revision30140.
Attached Files


has duplicate 0025906 closedJonas Maebe runtimeerror stdout stderr 


Marco van de Voort

2010-09-04 15:28

manager   ~0040801

(I agree in so far that it at least should be possible to change to stderr)


2014-03-25 19:18

reporter   ~0073968

since (at least) 9 years there are contrary opinions to the question,
whether r.e.m. (runtime error messages) from programs
(mainly, but not only: console programs)
that are generated by freepascal,
should go to stdout or stderr.
look at the following three cited issues, with comments from me:

> 0005620 descr: In Linux it would be nice to redirect the error
> 0005620 descr: messages to the stderr instead of stdout.

not only in linux. also in other unixes, msdos, mswin.

> 0005620 notes: Added option -vz
> 0005620 closed + fixed, 2005, v.1.9.6

very good. but, why did this option disappear later?

- - - -

> 0012996 notes: (Maebe) All run time error handling in the RTL uses stdout.

assert-messages go to stderr (without sysutils).
why is the handling different?

> 0012996 notes: (Maebe) Changing this to stderr would break
> 0012996 notes: backwards compatibility for little gain.
> 0012996 closed + won't fix, 2009, v.2.2.2

'compatibility': why do you not offer both alternatives?
'little gain': (see below)

- - - -

> 0017346 notes: (van de Voort) I agree in so far that it at
> 0017346 notes: least should be possible to change to stderr
> 0017346 new + open + tweak, 2010, v.2.4.0

very good. but, why has this idea not been realized in the last 4 years?

- - - -

of course a human can differentiate between r.e.m. and actual output
in the output of a freepascal-program.
but how can the differentiation happen,
if this output is processed by a (other) program?
an important example are (unnamed) pipelines
in command-lines of the form
      prog1 | prog2 | ... | progN .
in such cases freepascal-programs are unusable (as long as
they do not differentiate between r.e.m. and actual output).
therefore I can not understand Mr.Maebe's 'little gain' (0012996).

I hope I have shown convincingly the importance of the
request 'r.e.m. --> stderr',
and that the idea of Mr.van de Voort (0017346) will soon be realized.

Jonas Maebe

2014-03-25 21:44

manager   ~0073974

Last edited: 2014-03-25 21:45

View 2 revisions

Bug report 0005620 was interpreted differently from what the submitter probably intended. The "fix" was an option (-vz) to let the compiler write its error messages to stderr. It didn't change anything to how compiled programs behave. That option still behaves the same today as it did back then.

Reinier Olislagers

2014-09-24 08:59

developer   ~0077580

Any news on this? Getting error output to stderr sounds like a sensible thing to do, especially useful when running FPC programs as external processes (*cough* as fpcup does *cough*)


2015-02-15 21:36

reporter   ~0081115

is there something new?
(think of usability of fpc-prog's (mainly: non-gui) in pipelines.
 but I recur. see note 0073968.)

Thaddy de Koning

2015-02-16 18:49

reporter   ~0081140

Last edited: 2015-02-16 18:51

View 2 revisions

Since the original "fix" doesn't fix pipe behavior.
The request was to write errors (and or exceptions) to stderr.
Exceptions should imo be handled in code and in isolation from pipe in/out, but errors should be written to stderr.

Michael Van Canneyt

2015-03-08 10:49

administrator   ~0081719

I changed the default to write unhandled exceptions to StdErr.

The behaviour is controlled by a boolean in SysUtils:
Which is by default set to true. Those that want it can revert to the old behaviour by setting this variable to False.

Issue History

Date Modified Username Field Change
2010-09-04 15:17 Benito van der Zander New Issue
2010-09-04 15:28 Marco van de Voort Note Added: 0040801
2010-09-04 15:35 Jonas Maebe FPCOldBugId => 0
2010-09-04 15:35 Jonas Maebe Severity major => tweak
2014-03-23 19:23 Jonas Maebe Relationship added has duplicate 0025906
2014-03-25 19:18 hapr35 Note Added: 0073968
2014-03-25 21:44 Jonas Maebe Note Added: 0073974
2014-03-25 21:45 Jonas Maebe Note Edited: 0073974 View Revisions
2014-03-26 08:54 Reinier Olislagers Tag Attached: output
2014-03-26 08:55 Reinier Olislagers Tag Attached: Exception
2014-09-24 08:59 Reinier Olislagers Note Added: 0077580
2014-10-16 13:58 Michael Van Canneyt Assigned To => Michael Van Canneyt
2014-10-16 13:58 Michael Van Canneyt Status new => assigned
2015-02-15 21:36 hapr35 Note Added: 0081115
2015-02-16 18:49 Thaddy de Koning Note Added: 0081140
2015-02-16 18:51 Thaddy de Koning Note Edited: 0081140 View Revisions
2015-03-08 10:49 Michael Van Canneyt Fixed in Revision => 30140.
2015-03-08 10:49 Michael Van Canneyt Note Added: 0081719
2015-03-08 10:49 Michael Van Canneyt Status assigned => resolved
2015-03-08 10:49 Michael Van Canneyt Fixed in Version => 3.1.1
2015-03-08 10:49 Michael Van Canneyt Resolution open => fixed
2015-03-08 10:49 Michael Van Canneyt Target Version => 4.0.0
2015-08-30 22:47 Joost van der Sluis Fixed in Version 3.1.1 => 3.0.1
2019-12-05 16:04 Michael Van Canneyt Build 2.4.0-2 [2010/02/20] => 2.4.0-2 [2010/02/20]
2019-12-05 16:04 Michael Van Canneyt Target Version 4.0.0 => 3.2.0
2019-12-05 16:04 Michael Van Canneyt FPCTarget => -